Hi all
I am getting hiss from the preamp of my Trace ElliotGP12 SMX bass amp
It has already been checked but i was wondering if swaping the "old" opamps in the preamp would do something for lowering the noise (they are all socketed)
There is one TL072CP at the input and several TL074CN for the EQ and compressor section
Thanks
schematics attached
I am getting hiss from the preamp of my Trace ElliotGP12 SMX bass amp
It has already been checked but i was wondering if swaping the "old" opamps in the preamp would do something for lowering the noise (they are all socketed)
There is one TL072CP at the input and several TL074CN for the EQ and compressor section
Thanks
schematics attached
Hi, this belongs in the Instrument Amps section.
Rather than thinking in terms of changing all the op amps, please consider finding which one has gone noisy and just replace that one. It could be a noisy tube too.
Use the controls to isolate the problem. Turn the tube/solid state blend control back and forth. Does it affect the hiss? Turn the input gain up and down, does that affect the hiss? Turn the shape switch off and on, does that affect the hiss? Does the graphic EQ affect the hiss? And the graphic EQ in/out switch?
Any control that affects the loudness or tone of the hiss is after its source.
Rather than thinking in terms of changing all the op amps, please consider finding which one has gone noisy and just replace that one. It could be a noisy tube too.
Use the controls to isolate the problem. Turn the tube/solid state blend control back and forth. Does it affect the hiss? Turn the input gain up and down, does that affect the hiss? Turn the shape switch off and on, does that affect the hiss? Does the graphic EQ affect the hiss? And the graphic EQ in/out switch?
Any control that affects the loudness or tone of the hiss is after its source.
The hiss is starting as soon as I set the input gain to a correct level or my bass
Then the hiss increases when I go from solid state to tube in the input blend section
And so on when switching the differrent options (pre-shape and EQ)
No increase in hiss when dealing whith the low or high compression but only with the Eq balance knob in that Compressor section
According to the schematis, should it it help to change the 2 caps (C3 and C4 of 10uf) to a higher value (1000uf) to help filtering high frequencies?
Thanks
Then the hiss increases when I go from solid state to tube in the input blend section
And so on when switching the differrent options (pre-shape and EQ)
No increase in hiss when dealing whith the low or high compression but only with the Eq balance knob in that Compressor section
According to the schematis, should it it help to change the 2 caps (C3 and C4 of 10uf) to a higher value (1000uf) to help filtering high frequencies?
Thanks
Replacing C3 and C4 will make no appreciable difference. Have you tried a new ECC83? Check by replacement R221. The wiper of R15 will affect the gain of IC1 and may be a possible issue, causing more noise from IC1 but not very likely.
The tube is a new one; Do you mean replacing R2 and R21. What do you mean by the wiper of R15? excuse my poor understanding and electrical knowledge!
Hi,
Many moons ago I replaced the input TL072 with a NE5532
in my Sessionette bass combo. Definite noise improvement,
and as I recall it sounded somewhat less "hashy".
I retained the TL074's used in the rest of the preamp.
rgds, sreten.
Many moons ago I replaced the input TL072 with a NE5532
in my Sessionette bass combo. Definite noise improvement,
and as I recall it sounded somewhat less "hashy".
I retained the TL074's used in the rest of the preamp.
rgds, sreten.
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Hi,
However looking at the schematic the first TL072
is not used as an input, so changing it will have
much less effect presumably than I experienced.
rgds, sreten.
However looking at the schematic the first TL072
is not used as an input, so changing it will have
much less effect presumably than I experienced.
rgds, sreten.
Have you tried another ECC83? Most Chinese ECC83s tend to be pot luck on noise. Try and source the Sovtek 12AX7WA they tend to be nice and quiet. R221 is the anode load resistor and is known for drifting and changing value.If you look at the schematic R15 is the volume pot and the wiper is connected to pin 2 of the op amp. As the resistance reduces whist lowering the volume, the gain of the op amp increases.
Don't jump in at the deep end, it is most likely to be a noisy valve.
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